The present invention relates to a process for manufacturing TFT liquid crystal displays and, more specifically, to a process for manufacturing pixel electrodes with rough surfaces for serving as the reflection members of TFT-LCD devices.
With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in electrical products, such as PDAs, laptops, cellphones, high resolution television sets, etc. due to advantages as smaller size, portability, and lower power consumption. Particularly the up-to-date reflective LCD device is usually performed by utilizing the reflection of light incident from outside, wherein the pixel electrodes made of metal materials are applied to serve as reflection members. Thus the light reflected from the pixel electrode performs desired images on the displays through liquid crystal molecules and color filters. The reflective type liquid crystal display which does not require a backlight has been vigorously developed due to the advantages such as power saving, thin and lightweight. In addition, since members for the backlight are not necessary, the cost may be reduced.
Notedly, the deeply concerned and important key point is how to promote efficiency of light reflection because the light source of the reflective type LCD comes from the external illumination. In prior art, polarizing plates are introduced to adjust the phases of incident lights for increasing reflection intensity. However, it is not practical to apply the additional polarizing plates into the reflective type LCD. Another solution is to fabricate the pixel electrodes with rough surface for serving as the reflection diffusers for completely utilizing external illuminations, promoting efficiency of reflections and increasing contrasts.
Please refer to FIG. 1, the cross-sectional view of TFT-LCD with rough reflection fabricated by prior art is shown. The related process comprises follow steps. A gate structure 12 is defined on a glass substrate 10 first. Then an insulating layer 14 is deposited on surfaces of the gate structure 12. A semiconductor layer 16 such as amorphous silicon, a doped silicon layer 18 and a metal layer are sequentially formed on the gate structure 12. Next a photolithography procedure is performed to define a drain structure 20 and a source structure 22 to fabricate a thin film transistor 24.
After the thin film transistor 24 is fabricated, an additional step is performed to form plural bumps 26 made of photoresists in the areas for defining pixel electrodes later. Next a passivation layer 28 such as polymer material is coating onto the bumps 26. And a pixel electrode 30 is formed above those layers. Thus, the reflection efficiency is promoted due to the pixel electrode 30 having a rough and uneven surface. Next another thicker passivation layer 32 is formed on the surfaces of the pixel electrode 30 and the thin film transistor 24 for the purpose of planarization.
Please refer to FIG. 2, the TFT-LCD with polarizing plates is shown. After defining the thin film transistor 24 and the pixel electrode 30, the thicker passivation layer 32 is deposited on these devices and layers for planarization. Then a liquid crystal layer (not illustrated) and a color filter 34 are sequentially formed on the passivation layer 32. A polarizing plate 36 is fabricated on the color filter 34 to increase reflection intensity. However the additional polarizing plate 36 leads to increasing cost and more complicated process.
The one objective of the present invention is to provide a method for manufacturing a TFT-LCD device having pixel electrodes with rough surfaces for serving as reflection members.
Another objective of the present invention is to provide a method of forming pixel electrodes with rough surfaces.
A method of forming a TFT-LCD device with a rough pixel electrode for serving as the diffuser member is disclosed hereinafter. The method comprises the following steps. First, a first passivation layer is formed on the transparent insulator substrate to cover the transistor. The first passivation layer is etched to form contact holes to expose a drain structure and simultaneously to define a plurality of ridge bumps in a display area on the transparent insulator substrate. Then, the ridge bumps are etched to make surfaces thereof rough. A pixel electrode is formed on the first passivation layer and the ridge bumps to connect electrically to the drain structure, wherein the pixel electrode formed along the rough surfaces of the ridge bumps has a rough diffuse surface.